The Surrender of Mary

When it comes to the first Christmas, God sovereignly orchestrates it all, and yet He works through ordinary people to bring the Savior to Earth. There is no better example of this than Mary. Without her total surrender, the arrival of Jesus and the miracle of the virgin birth would never have happened.  How could an all-powerful God let His grand plan "hang in the balance" with a humble, powerless teenage girl from Nazareth?